1. Field of the Invention
The invention pertains generally to the diagnosis of multi-cylinder engines in which operating characteristics of an engine specific to individual cylinders are measured and, particularly, to a method and apparatus for matching measurements of such characteristics taken during suppression of the ignition system to individual cylinders.
2. Related Art
In the measurement of cylinder-specific operational characteristics or traits of an internal combustion engine there is always the problem that matching of measurements to their respective cylinders requires special steps to obtain clear and unambiguous identification of the cylinders. However, the identification should not require any significant outlay in the preparation and performance of the measurements.
In connection with spark-ignition engines, methods are known for allocating measurements t corresponding cylinders taken with ignition permitted. For example, compression characteristics of engine cylinders may be measured by measuring variations in current draw required of a starter motor to turn over an engine. The measurements are allocated by detecting ignition pulses in a predetermined cylinder and then allocating measurements pursuant to a known firing order.
Another known method, employed particularly in connection with diesel engines, uses marks on rotating parts of crankshafts or camshaft drives for determining ignition top dead center (TDC) of a selected cylinder. Measurements are allocated by noting which cylinder has reached TDC when a measurement is taken.
However, a problem arises with the methods discussed when the measurements are to be carried out with ignition suppressed or where no marks for indicating ignition TDC or similar reference points are present on an engine. Recognition of ignition TDC of cylinders is no longer possible and it is almost impossible to match measurements to cylinders.
In connection with testing of diesel engines, a method and apparatus have been known in which before measurements are taken in which fuel injection is reduced by hand to a point where it is insufficient for ignition to take place in an engine, but where it is sufficient to deliver a detectable injection pulse to a sensor clamped onto a fuel injection pipe of a selected cylinder. However, a drawback often arises in that either partial ignition still occurs or that there is an insufficient injunction pulse to trigger the sensor.
German published application OS No. 2 207189 discloses a method and apparatus in which characteristics are measured starting with any cylinder, stored in accordance with a known firing order and then associated with their respective cylinders. During a first ignition cycle with an ignition coil short-circuited, within the course of a falling edge of a contact breaker pulse, successive peak values of a cylinder-specific operating characteristics waveform are stored in successive locations in an analog store. During a second ignition cycle with the ignition coil switched on, a first peak pulse arising in a predetermined cylinder is fed to a first stage of an appropriately constructed ring counter. During the second cycle, a falling edge of the first ignition pulse is delayed until the end of a third ignition cycle. Starting from a stage of the ring counter marked after the end of the third ignition cycle, the stored measurements are then delivered in sequence through an associated relay selector by means of the ring counter to a circuit programmed in accordance with the known firing order. And thus, the measurements are identifiable with respective cylinders.
However, this method and apparatus have the disadvantage that on the one hand there is required a high outlay for circuits to put them into practice and on the other hand the marking of measurements with the ignition suppressed, requires detection of the contact breaker pulses, which means an additional outlay for detection circuits. Moreover, this method and apparatus cannot be applied to all engines.